A conductor is a substance that allows the flow of a charge, an electrical current, in one or more directions. Metal is commonly used as a conductive material. The resistance of metallic conductors decreases gradually as its temperature is lowered down to absolute zero. Absolute zero is taken as −273.15° on the Celsius scale, which equals −459.67° on the Fahrenheit scale. Below absolute zero certain substances achieve superconductivity, where the electrical resistance, the opposition to the flow of electrical current in the substance, vanishes, and the magnetic flux fields are expelled. This magnetic field expulsion is why you will often see and hear about magnetic levitation in reference to superconductivity. But unlike a pair of repelling magnets, superconductors are unaffected by magnetic flux flow, thus a superconductor can levitate magnets in a very stable way. This means that when kept below the critical temperature, absolute zero, an electrical loop of superconductive wire, can persist forever, without a power source.
Superconductive magnets are some of the most powerful magnets on Earth. They are used as plasma confining magnets in tokamaks, as beam steering magnets in particle accelerators, and also in MRI machines. Superconductive magnets are also used for magnetic separation, which is useful in the pigment industry, and in large wind turbines. Recently, superconductors are engineering into electrical circuits, as well as the RF and Microwave filters of cell phone base stations. Superconductors are also used to maintain super currents in Josephson junctions, which are the fundamental pieces of superconducting quantum interference devices, the most sensitive magnetometers yet invented.
The future of superconductivity looks promising, with applications in electric power transmission, smart power grids, transformers, electric motors, power storage devices, magnetic levitation devices, superconductive transmission lines, fault current limiters, and conducting magnetic refrigeration. However, superconductivity is sensitive to moving magnetic fields, so devices which rely on direct current will be easier to engineer than those relying on alternating current. So far, there have been Nobel Prizes awarded in five different years, to twelve scientists, for investigations involving superconductivity.